Previous work with macrolides suggests that this class of agents may have activity against cryptosporidiosis. The aims of this study are to: (1)evaluate the safety and efficacy of ascending doses of clarithromycin (2)compare the absorption and tolerability of the tablet and liquid forms of cla rithromycin; and (3)evaluate the impact of malabsorption, as measured by d-xy-lose absorption, on the bioavailability and efficacy of clarithromycin for AID related cryptosporidial enteritis.